Known portable mixing plants for producing asphalt and the like do not consistently obtain a homogenous mixture of aggregate and additives in the blending and mixing process. These problems arise from inconsistent flow of the aggregate, dry additives and liquid additives into the mixing chamber as well as changes in the mass balance of the mixing chamber. Resulting mixtures are not homogenous, thereby producing an undesirable finished product. In part, the inconsistent flow can be attributed to the difficult process of dispensing solid matter in a steady-state fashion. The discrepancies in the mixtures are accentuated in the portable mixing plant by the rugged nature of the terrain where the plant is normally used. The general presumption in the present versions of the portable mixing plant is of a steady-state model in the mixture process, but the present day control systems are not designed to handle the transient dynamic models that constitute the actual mixing process.
Prior art attempts to solve this problem have involved volumetric metering of the aggregate or the additives. One such device is a plant made and sold by Aran of Wacol, Brisbane, Australia under the name Aran ASR Continuous Mixing 280C. Although such techniques provide some improvement in the final product consistency, they are difficult to use in practice and are quite cumbersome to transport. There thus remains a long-felt need to overcome these and other problems associated with such plants.